The catalytic mechanism offers an efficient tool to produce crystalline semiconductor nanowires, in which the choice, state, and structure of catalysts are active research issues of much interest. Here we report a novel solution-solid-solid (SSS) mechanism for nanowire growth catalyzed by solid-phase superionic conductor nanocrystals in low-temperature solution. The preparation of Ag2Se-catalyzed ZnSe nanowires at 100-210 °C is exampled to elucidate the SSS model, which can be extendable to grow other II-VI semiconductor (e.g., CdSe, ZnS, and CdS) nanowires by the catalysis of nanoscale superionic-phase silver or copper(I) chalcogenides (Ag2Se, Ag2S, and Cu2S). The exceptional catalytic ability of these superionic conductors originates from their structure characteristics, known for high-density vacancies and fast mobility of silver or copper(I) cations in the rigid sublattice of Se(2-) or S(2-) ions. Insights into the SSS mechanism are provided based on the formation of solid solution and the solid-state ion diffusion/transport at solid-solid interface between catalyst and nanowire.

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First-order solid–solid phase transition of crystalline solids at the nanoscale has attracted an increasing interest in solid-state physics and chemistry, which can be used to alter the properties of materials without changing chemical compositions. Herein, we report the results of our comparative studies on phase transitions between tetragonal (t), orthorhombic (β), and cubic (α) polymorphs in Ag2Se nanocrystals. A significant discrepancy in stability and phase transition behavior is determined for t-Ag2Se nanocrystals, which were prepared separately by two different methods. Differential scanning calorimetry (DSC) and variable-temperature XRD studies reveal that the t-Ag2Se nanocrystals prepared by the oleylamine (OLA)-mediated method show a highly temperature- and time-sensitive metastability and undergo a t → β → α → β phase transition during the thermal cycling, in which the t → β transition is exothermic and irreversible, whereas the β → α transition is reversible. Similarly, the reversible β → α structure transition is detected in the β-Ag2Se nanocrystals, which were also prepared using the OLA-mediated method with different post-treatment manners and stabilized conditions. In contrast, the t-Ag2Se nanocrystals prepared by the PVP-assisted solvothermal method are more stable and exhibit a direct, reversible t → α phase transition without undergoing the β phase; however, when heated to a high temperature, for example, ≥250 °C, the stability of the t phase and the reversibility of the t → α transition will be destroyed due to the sintering and size increase of the sample, which is confirmed by the determination of the t → α → β phase transition in the DSC cycle. The formation of the t phase is attributed to the α → t structure transformation with the temperature cooled from synthetic temperatures (160–220 °C) to room temperature. Moreover, the reasons for the difference in the stabilities and phase transitions of t-Ag2Se nanocrystals prepared in our two methods are discussed based on the influences of size, surface (or shape), and defects on the thermodynamics and kinetics of a solid–solid structure transformation.

Solar-driven water oxidation is the key step for overall water splitting that efficiently harvests and converts solar energy into fuels; the development of a highly efficient photocatalyst that can mediate water oxidation has become an appealing challenge. Herein, we report a facile two-step process to decorate silver phosphate (Ag3PO4) particles on different types of graphitic carbon nitrides (g-C3N4) as composite photocatalysts for water oxidation. For all the Ag3PO4/g-C3N4 materials, an in situ Z-scheme is created by the generation of Ag nanoparticles which act as a cross-linking bridge between Ag3PO4 and g-C3N4 in the composite, resulting in better charge separation and higher catalytic performance. A detailed analysis emphasizes the importance of the g-C3N4 on the chemical, photophysical, and catalytic properties of the composite materials. Our results show that the alteration of the morphology dominates the performance of the composite materials.